Cannot build FFmpeg on CYGWIN

[Carlo Bramini]

I cloned the latest development sources and I tried to build them on CYGWIN. Unfortunately, I got these errors:

src/libavdevice/gdigrab.c: In function ‘gdigrab_read_header’:
src/libavdevice/gdigrab.c:252:12: error: implicit declaration of function ‘utf8towchar’ [-Werror=implicit-function-declaration]
  252 |         if(utf8towchar(name, &name_w)) {
      |            ^~~~~~~~~~~

CC      libavcodec/mf_utils.o
In file included from /usr/include/w32api/dshow.h:33,
                 from src/libavcodec/mf_utils.h:32,
                 from src/libavcodec/mf_utils.c:25:
/usr/include/w32api/strsafe.h: In function ‘StringGetsExWorkerW’:
/usr/include/w32api/strsafe.h:1859:18: error: ‘WEOF’ undeclared (first use in this function); did you mean ‘EOF’?
 1859 |           if(ch==WEOF) {
      |                  ^~~~
      |                  EOF

but hopefully they are easy to fix.

1) Since src/libavdevice/gdigrab.c is compiled also in CYGWIN then libavutil/wchar_filename.h must be included also for it in addition to _WIN32.
2) WEOF requires to manually include wchar.h under CYGWIN. When compiling also under MinGW-w64, this tiny addition did not make any difference in my tests.

I attached a patch with my solution.

[Carlo Bramini]

The patch